Research On Key Technologies Of ?-? Modulator Based On SAR Quantizer

In recent years,wireless communications and mobile computing are steadily developing at a higher rate,and higher requirements are placed on the accuracy and power consumption of integrated circuits.Taking reducing power consumption,saving area and improving accuracy as the starting point,a SAR quantizer-based?-?(also called Sigma-Delta)modulator hybrid structure is designed.This structure uses SAR quantizer instead of traditional Flash ADC type quantizer to realize quantization processing.Compared with the traditional structure,the SAR quantizer does not require multiple comparators,does not have the problem of component mismatch,has a simple structure and can reduce overall power consumption.In this paper,the oversampling technology and noise shaping technology of Sigma-Delta modulator are studied,and the structural characteristics of single-loop,cascade,feedforward,feedback,one-bit and multi-bit modulators are analyzed,and the outstanding advantages of Sigma-Delta modulator in high-precision audio field are clarified.The relationship between modulator performance and modulator order,oversampling rate and quantizer bit number is summarized,and the second-order integrator and five-bit quantizer are determined to be used.On this basis,a behavioral model of the Sigma-Delta modulator was built to verify the performance of the modulator.The circuit design of the proposed second-order five-bit quantized Sigma-Delta modulator is carried out using 0.18?m CMOS process,which mainly includes a quantizer circuit and an integrator circuit.The quantizer is composed of capacitor array,SAR comparator and logic circuit.The capacitor array adopts a multiplexing structure,which can eliminate the first-stage sampling capacitor of the integrator and simplify the circuit structure.The SAR comparator uses a differential input structure,with lower common-mode voltage and higher quantization accuracy.The integrator is composed of a transconductance operational amplifier and a switched capacitor.The feedforward structure is adopted as a whole to avoid distortion of the operational amplifier in the integrator.At the same time,the first-stage integrator does not require sampling capacitors,further saving chip area.Use Cadence Spectre software to verify each sub-module and overall module of the modulator,including quantizer module,integrator module,overall modulator module and overall clock module.The final simulation results of Sigma-Delta modulator circuit are as follows:under the conditions of 1.8V power supply voltage,3.2MHz sampling frequency and 128 oversampling rate,the signal-to-noise ratio is 98.5d B,and the effective number of bits is 16.07bits.The comparator,amplifier,common mode feedback,reference voltage source and overall layout of the modulator were designed and tested,and the effective area of the overall layout is 0.56mm~2.